[PATCH] PCI Hotplug/powerpc: module build break

The RPAPHP hoplug driver will not build as a module, because it calls
on a pcibios routine which is not exported. This exports the symbol.
Problem reported by Olaf Hering <olh@suse.de>

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>